Parameters

Values assigned in the various equations that represent climate processes in (climate) models.

In detail

It is not always possible to incorporate every physical process that operates in the climate system into a climate model. This may be because the processes involved operate at a spatial resolution that is too fine to be incorporated into a model or due to computational constraints. Consequently, parameterisation schemes are developed to partially address this issue. A fundamental requirement in a parameterisation scheme is the specification of likely values (or a range of likely values) that a particular parameter might take. These parameterisation schemes relate the larger scale processes that are represented in the climate model to the smaller scale (or sub-grid scale) processes through mathematical equations. Within these equations values need to be assigned to the individual parameters. This process often involves a mixture of theory, observations, experimentation and expert judgement, and as a result the definition of parameter values is seldom precise enough to be able to assign accurate values. This is the parameter error component of modelling uncertainty.

• More details about parameters in climate models are given in Box 2.1 in the UKCP09 Climate change projections report. A commentary about the strengths and weaknesses of climate models is given in Annex 3.

• An overview of how probabilistic projections are created and presented in UKCP09 is described in Box 3 of the UKCP09 Briefing report. More details are provided in Chapter 3 of the UKCP09 Climate change projections report, including an overview of the methodology in Section 3.2.12.

• A comparison of the UKCP09 methodology with an alternative method is described in Annex 2.3, and summarised in Box 4 of the UKCP09 Briefing report.